The in vivo delivery of a biologically active agent within the body of a patient is common in the practice of modern medicine. In vivo delivery of biologically active agents is often implemented using medical devices that may be temporarily or permanently placed at a target site within the body. These medical devices can be maintained, as required, at their target sites for short or prolonged periods of time, delivering biologically active agents at the target site.
In accordance with typical delivery strategies, a therapeutic agent is provided within or beneath a biostable or biodisintegrable polymeric layer that is associated with a medical device. Once the medical device is placed at the desired location within a patient, the therapeutic agent is released from the medical device with a profile that is dependent, for example, upon the loading of the therapeutic agent and upon the nature of the polymeric layer, among other factors.
For instance, in the past ten years stents have emerged as a prime therapy for arthroclerosis because they counteract the effects of intimal hyperplasia from balloon injury. Unfortunately, in-stent restenosis is a disease that may occur from the stent injury to the vessel wall. Drug eluting stents have a coating over the stent to release a drug at a prescribed rate for a given duration to counteract the effects of in-stent restenosis. The coating on the stent is in contact with the delivery system (e.g., balloon) along its inner diameter and in contact with the vessel wall along its outer diameter. It is advantageous to optimize the properties of the polymeric coating so as to control the release of drug, have optimum biocompatibility against the vessel wall, and be mechanically compatible with the surface of the balloon. Examples of drug eluting coronary stents include commercially available stents from Boston Scientific Corp. (TAXUS), Johnson & Johnson (CYPHER), and others.